Many electronic devices include a battery life indicator to provide an indication of how much time a user can continue to use the device before the battery runs down. Consumers expect an accurate indication of current battery life in battery powered electronic devices.
Conventional battery life detection circuits can use analog current measurements or voltage measurements to determine the battery life. Analog current measurements tend to be very accurate and provide consumers with a relatively reliable indication of battery life over the duration of the electronic devices usage. Such measurement circuits often determine the remaining charge stored by the battery as a function of the measured current, which can be characterized for the particular battery. However, this accuracy comes at a cost of larger and more expensive electronic devices and reduced battery life.
In electronic devices, such as notebook computers, PDAs (personal digital assistant), portable music players, and mobile (cellular or digital) phones, the additional circuitry required to measure current cannot be accommodated without increasing the overall size of the device. Accordingly, such portable devices often measure voltage to determine battery life instead. While voltage measurement circuitry is often cheaper and typically occupies less space and uses less hardware than analog current measurement circuitry, such voltage measurement circuitry often produces a less accurate battery life indicator.
Voltage measurement circuitry measures the voltage level over time, detecting a distinct drop off when the remaining charge of the battery approaches zero volts. In some instances, the measurement circuitry generates a signal in response to the abrupt change in the voltage level, which is reflected by an abrupt change in the battery life indicator, such as a rapid change from over fifty percent remaining to under ten percent in a matter of minutes for rechargeable batteries that typically last for several hours. On portable computing devices and cell phone devices, the voltage measurement circuitry does not reflect consistent power consumption, which means that the battery indicator may not accurately reflect the remaining battery life. Such voltage-measurement-based battery indicators can change very little over a period of time and then can change very abruptly when the battery is almost completely discharged, causing the battery life indicator to change from two hours remaining to, for example, fifteen minutes remaining over the course of a few minutes.
In the following description, the use of the same reference numerals in different drawings indicates similar or identical items.